This invention relates generally to controlling video formats, for example in graphics accelerators or controllers that enable text and/or graphics to be displayed on a display such as a television receiver, a monitor or a liquid crystal (LCD) display, as examples.
Conventional displays such as monitors and liquid crystal displays (LCD) used in connection with electronic devices such as computer systems, often use the RGB color space. In the RGB color space an image may be resolved into pixels having red, green and blue intensity values.
A video adapter may generate the video signal for a video display. A graphics controller or accelerator may be part of the video adapter and may allow access to a video adapter buffer, or video memory, that stores data such as graphics or character data. Graphics controllers or accelerators work in the RGB color space. When it is desired to work in a video format such as a color space other than RGB, the non-RBG video is converted to the RGB color space and then is provided to the graphics controller which thereafter produces an RGB output.
A variety of other color spaces are used. For example, the U.S. television broadcasting system generally uses the National Television Systems. Committee (NTSC) standard which uses the YUV color space. British television broadcasting uses the phase alternate line or PAL system which makes use of the YUV color space. French television broadcasting uses the Sequential Coleur Avec Memoire (SECAM) system which uses the YDrDb color space. The International Consultative Committee On Broadcasting, known as ITU-R, has developed a digital color system known as YCrCb or ITU-R-BT.601 or CCIR-601. High Definition Television (HDTV) uses the YCrCb color space as well, according to the Advanced Television Systems Committee (ATSC) Guide to the Use of the ATSC Digital Standard, ATSC Doc. A/54, 4 Oct. 1995.
Thus, there are a number of different color spaces that may be utilized with television systems, which do not operate in the RGB color space. Generally, the conversion to the RGB color space may involve a simple mathematical operation such as simple multiplying and shifting. Known equations are available to convert any of the PAL, NTSC, SECAM or ITU-R-BT.601 color spaces to or from the RGB color space. Software is generally known for making these conversions as well.
Graphics controllers that receive non-RGB inputs may provide output signals to a device which does not use the RGB format. However, the graphics controller may only work with RGB color space input signals. Therefore, a non-RGB input signal may be converted to the RGB format. Similarly, the output signal from the graphics controller may be converted back to a non-RGB format in order to be displayed in a non-RGB format, on a conventional television receiver, for example. In some instances, the original input signal is initially converted from a non-RGB to RGB and then back to the non-RGB format.
Thus, there is a need for systems for controlling video formats that operate more flexibly with the variety of available color spaces and that are more efficient in handling color space conversions.